Powertrain, generic (extended)

P231E Cylinder 11 Air-Fuel Ratio Imbalance - Adjustment At Limit During Balance

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P231E belongs to cylinder 11 and can only come from twelve-cylinder engines, V12 or W12. The per-cylinder fuel trim for cylinder 11 sits at its limit during balancing. There is no public manufacturer description and no NHTSA bulletin. On such engines six cylinders share each bank, so one deviating cylinder shifts the bank sensor signal only slightly; that is one reason CARB accepts a bank or misfire code where a single cylinder cannot be resolved. Mercedes' M177 bulletin for the cylinder 7 code of the same series shows that a software update can be the real remedy. In the workshop, compare the trim values and misfire counts of cylinder 11 (P0311, P21A6) with its neighbours before the injector is replaced.

Likely causes

Injector of cylinder 11 delivering too much or too little (deposits, wear)

Air leak at the intake port or injector seal of cylinder 11

Valve of cylinder 11 not sealing (worn seat or guide), low compression

Poor contact at the connector of injector 11

Symptoms

Check engine light on
Rough idle, possibly misfire on cylinder 11
Higher fuel consumption or exhaust smell

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€0–1,500

Time0.5–6 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel injector cyl 11intake manifoldcylinder compression

References: law.cornell.edu, static.nhtsa.gov.